Fusarium is a group of soil-borne fungi with many different species. Fusarium is widespread and can infect a range of host crops. Many species are considered weak pathogens and can only infect wounded or stressed host plants.
Life cycle and appearance of Fusarium wilt
Fusarium oxysporum has many different formae speciales which are each selectively pathogenic on a limited number of crops. Even within one crop, different formae speciales may occur and cause different symptoms. Fusarium oxysporum is the only Fusarium that actually grows inside the vessel system of the host plant and spreads upwards inside the plants. The other species are dispersed upwards on the outside of the plant.
Most Fusarium species only make asexual spores. Some also produce ascospores. The Fusarium oxysporum life cycle, is similar to that of most Fusarium species. Fusarium overwinters for many years in the soil and on crop residues of infected plants as chlamydospores (thick walled mycelium cells) or mycelium. Survival is also possible on seed, greenhouse structures, tools and machinery. Primary infection is either seed-borne or takes place as infection of the roots at the root tip or in small wounds, for example where lateral roots branch off from the tap root.
Fusarium fungi cause vascular wilt, root rot, foot and stem rot, leaf lesions, fruit rot, head blight in cereals and post-harvest decay.
Fusarium oxysporum is the species causing vascular wilt. First the leaves turn yellow and wilt, mostly on one side of the plant. Finally, the whole plant wilts. Other symptoms are brown discolouration of the xylem vessels which can be seen when the stems are cut. In banana, whole plantations may die and the soil may not be suitable for planting for many years to come.